Hetero-hexanuclear ruthenium-nickel complexes containing 2, 2'-biimidazolate dianion . Synthesis, ESI-MS and X-ray structure characterization

Abstract

Efficient and direct synthesis of hexametallic complexes, [{(pap)₂ Ru (bimm)}₄ M₂] l(ClO₄)₄ (pap =2 -(phenylazo) pyridine, M = Ni [<b>2a</b>] and Cu [<b>2b</b>] ) based on the reaction of hydrated MCl₂ and [{(pap)₂ Ru (bimm)}₂Ag₂] (ClO₄)₂ is elaborated. Synthesis of the 2, 2'-bipyridine (bpy) analogue of [<b>2a</b>] is also described. Electrospray mass spectra of the complexes are analyzed which fully corroborate with their formulations. X-ray structure of a representative complex

[{(pap)₂ Ru (bimm)₂}₄ Ni₂] (ClO₄)₄, [<b>3a</b>] is reported. The structure consists of four octahedral [(bpy)₂Ru (bimm)] units arranged around the Ni₂-moiety in a propeller type arrangement. The separation between the two nickel (II) ions in this complex is 2.803(7) Å. The dependence of network topology on counteranions is also reported, which ultimately gives rise to a 2D sheet structure. The two nickel complexes [<b>2a</b>] and [<b>3a</b>] are diamagnetic and display resolved ¹H NMR spectra in dmso-<i>d</i>₆. These are intensely coloured and their visible range spectra are dominated by an intense transition (ε,37,000-38,000 <i>M</i>^-1cm^-1) due to Ru dπ→π (ligand) transition. These complexes display multiple cyclic voitammetric responses, or which the responses at anodic potentials are ascribed to oxidations of the ruthenium centres.